Mastitis is inflammation or infection of breast or udder tissue, and can be classified as puerperal and nonpuerpural mastitis. Puerperal mastitis is associated with pregnancy, breastfeeding or weaning and occurs frequently in lactating mammals, both in animals and humans. Nonpuerpural mastitis has no relation to lactation, but has very similar symptoms, and may occur for example after nipple piercing. It is estimated that up to 33% of lactating women suffer from mastitis. Although mastitis may occur at any time during lactation, occurrences peak during the second and third week postpartum. The majority of mastitis is caused by Staphylococcus infection, mainly S. aureus and S. epidermidis. Treatment often involves administration of antibiotics. Mastitis is highly undesired, as the composition of the breast milk alters during mastitis, e.g. an increased content of sodium and inflammatory mediators, which may interfere with the optimal nutrition breast milk provides for the infant. Furthermore, during mastitis, continuing breastfeeding may not be possible or may not be desired by the mother.